It is a common practice to blend polymeric rubber compounds with other compounds which may function as processing aids or impart desirable characteristics to the final product. Such other compounds include polymers which may be elastomers or non-elastomers, oils, plasticizers, and the like. For example, U.S. Pat. No. 3,632,540 to Unmuth et al discloses binary and ternary elastomer compositions based upon thermoplastic elastomeric block copolymers characterised as A-B-A copolymers. In this designation, the A and B blocks indicate nonelastomeric and elastomeric polymer blocks, respectively. As disclosed in Unmuth, the end blocks may take the form of alkenyl arenes and the elastomeric B block the form of polymerized conjugated dienes. The block copolymers may be "pure" block copolymers or "tapered" block copolymers. The elastomeric midblock sections can be formed essentially of any synthetic elastomer, preferably of an aliphatic conjugated diene, such as isoprene, methyl isoprene, butadiene, styrene-butadiene copolymers and butadiene-acrylonitrile. The elastomeric midblock sections may comprise copolymers of ethylene with C.sub.3 -C.sub.8 monoolefins, preferably C.sub.3 -C.sub.6 alpha olefins. As disclosed in Unmuth, suitable vinyl aromatic endblocks may be derived from styrene, vinyl toluene, vinylxylene, ethylvinylbenzene, isopropylstyrene, ethylvinyltoluene, tert.-butylstyrene or diethylstyrene. Copolymers containing at least 70 % weight vinylaromatics and 30% or less alpha-methylstyrene or esters of acrylic or methacrylic acid may also be employed.
The A-B-A type polymers thus described are blended with natural or synthetic waxes in the binary compound and, optionally in the ternary compounds, with certain resins which do not exhibit liquid-phase separation. Suitable waxes include natural or synthetic waxes such as paraffin wax, scale wax and polyalkylenes such as polyethylene, polypropylene, and blends and copolymers thereof. The resin in the ternary mixture is employed to enhance the blendability and viscosity of the block copolymer and wax mixture. Suitable resins include rosin, hydrogenated rosin, esters of rosin and hydrogenated rosin and dimerized rosin and esters thereof. Various other resins are also disclosed and, in addition, the elastomer compositions can contain other additives such as antioxidants, friction reducing additives, pigments and fillers, and various other synthetic rubbers, copolymers and homopolymers. The compositions may be employed in formulating coatings laminates, hot melt adhesives, and caulking compounds.
U.S. Pat. No. 4,369,284, to Chen discloses a gelatinous multicomponent elastomer composition based upon specific ABA triblock copolymers of the type disclosed generally in the aforementioned patent to Unmeth et al. Thus, Chen discloses a mixture of styrene-ethylene/butylene-styrene triblock copolymer and a plasticizing oil such as white petroleum oil or a synthetic liquid oligomer of polybutene, polypropene or polyterpene. The copolymer is characterized as having a styrene end block to ethylene/butylene center block ratio within the range of 31:69-40:60. A suitable copolymers is identified as Shell Chemical Company's Kraton G. 1651. Copolymers identified as Kraton G 1650 and G 1652 are characterized as too low in styrene content.
Yet another multicomponent elastomer mixture is disclosed in U.S. Pat. No. 4,377,655 to Himes. The compostion, which is employed in molded shoe soles, is based upon a mixture of a linear ABA block copolymer and a radial (A-B-).sub.x B-A block copolymer. The A blocks are monoalkynyl arene polymers having average molecular weights within the range of about 5,000-45,000 and the B blocks are elastomeric conjugated diene polymers having average molecular weights within the range of about 15,000-300,000. The compositions also contain a styrene-acrylonitrile copolymer and a vulcanized vegetable oil and may optionally contain a hydrocarbon rubber extending oil and a finely divided filler. The extending oils are characterized as paraffinic naphthenic oils having less than 30 weight % aromatics and viscosities within the range of about 100-500 SSU. Fillers which may be used include clay, talc, alumina, anhydrous silica, titaniumdioxide, carbon black calcium, calcium carbonate, and fibers such as polyester or acrylic fibers. The composition may also contain a minor amount of stearic acid.
U.S. Pat. No. 4,101,482 to Doss et al discloses a low tack sealant composition comprising a mixture of two block copolymers, modifying resin, and a filler. The block copolymers may be thermoplastic AB and ABA (AB).sub.n Y copolymers with A representing polyvinyl aromatic blocks and B poly conjugated diene blocks. Thus, the A blocks may be derived from styrene, methylstyrene, propylstyrene and vinylnaphthalene. The conjugated diene blocks are derived from C.sub.4 -C.sub.8 monomers which include 1,3butadiene, isoprene, 1,3-pentadiene, 2,4-hexadiene and 3-ethyl-1,3-pentadiene. The polymers preferably have A/B weight ratios within the range of 40/60-15/85. The modifying resin employed in the formulation is a normally solid resin such as a modified or unmodified rosin or rosin ester, esters of polymerized rosin, polyterpene resins, terpenephenolic resins, coumaroneindene resins, diolefinolefin resins, phenol-aldehyde resins, alpha-methyl styrene copolymers. Plasticizers include polyolefins such as polybutene, naphthenic, paraffinic or aromatic oils, various esters, and chlorinated hydrocarbons. Fillers disclosed in Doss et al include calcium carbonate, aluminum silicate, clay, talc, kaolin, barytes, mica, silica and mixtures thereof. Carbon black and titanium dioxide may also be added as pigments. The formulation may also include sterically hindered phenols and other antioxidants and antiozonants as stabilizers.
Many elastomeric polymers are readily subject to foaming to form cellular rubber products that may be either open celled or closed celled. Such products and their preparation are discussed by Bascom, R.C. "Cellular Elastomers" Rubber Age p. 576, July, 1964. Closed-celled products are employed in gaskets and other similar packing products since the void volume of the product is predominantly in the form of a discrete cells disposed throughout the product so that it is a relatively impermeable to gas flow. The cellular rubber products may be formed by decomposition of "blowing agents" such as halocarbons, e.g. trichlorofluoromethane, azodicabonate and hydyazine, or by the direct aeration of the molten rubber stock with an inert gas. In either case, nitrogen will usually be employed as the infusing gas in order to avoid loss of internal gas to the atmosphere.
U.S. Pat. No. 2,666,036 to Schwenke discloses a process of producing cellular rubber like products employing resins which are not in themselves elastomeric. Thus, the Schwence process involves the foaming of a liquid formulation of polyvinylchloride homopolymers or copolymers in a plasticizer oil which also contains a water insoluble salt of a fatty acid containing from 12 to 22 carbon items, specifically aluminum stearate. The foam is cured to provide a cellular plastic similar to rubber products such as sponge rubber or foam rubber.
U.S. Pat. No. 3,856,719 to Miyamoto et al discloses a process for producing foamed thermoplastic resin articles which are characterized as having good flexibility and elasticity. The product is produced from a formulation of low-density and high density polyethylene, together with a polystyrene type resin. This includes a mixture of polystyrene as the main component together with a rubbery polymer containing at least 50 % by weight of polystyrene or a copolymer of styrene with diene monomers, such as styrene-butadiene copolymer. Miyamoto also discloses use of nucleating agents to provide the desired cell size of the famed product. Suitable nucleating agents include a finely divided inorganic substances such as talc, clay, diatomaceous earth and silica. Also disclosed are organic substances such as the salt of citric acid and sodium bicarbonate which generate gases upon decomposition or chemically change at the extrusion temperature.